Frequency measuring circuit



April 19, 1949. J. A. RAJCHMAN ET AL FREQUENCY MEASURING CIRCUIT 2Sheets-Sheet 1A Filed April l, 1942 mi@ mae M Smb G hw .co NWJC... nHm..

B 8 Edwin .1w-4P] l Q-1 i. FI'fGnZa.

Friarh April 19, 1 949- J. A. RAJCHMAN ETALY 2,467,777

v FREQUENCY MEASURING CIRCUIT Filed April l, 1942 I 2 Sheets-Sheet 2nnfinn x am f J FIG.Z. NN N www w QQQMA attorney Patented Apr. 19, 1949A.. Goldberg,z.Haddon: Heights, ,N. J assignors to Radio, CorporationofAmerica,aacorporation. A

of Delaware.

Application yApril' 1f, .1942, Serial LNo'.j 4317,12GII` f 2.Claims...(Cl. Z50-27) Thisfinvention.. relates `generally tol frequency measuringcircuitsand particularly to a fre.`

quency measuring circuitin Which acurrent is derived' Which issubstantially` proportional. in amplitude to theaverage frequency of Yasignal applied. to the. input of thecircuit.

The invention utilizesa unique arrangement.

of .thermionic tube 4circuits including a high pass filter, one. or moresaturation amplifiers, a differentiating circuit, apeakampliiienand aVnovel` 10' remaining.'terminal-` of :the capacitor. 2I5con triggerycircuit,.as.we1l'as means forI damping the nectedito thecontrolelectrodemfxaepeakzamplif. diier'entiating circuit and thetrigger circuit. fieri; `x/liichxiselciasedatcuamplify.onlvstlzle@voltev Among the objects .ofthe invention are to proage:peaks er"r the.k applied. 'signa-1;- Theicathodefiw vide means forderiving a current or voltage proeircuitzof therpeaksamplierfincludesxacathode. portional in amplitude to the averageY frequency 15fresisto1f.22a f Voltagefacrossf this vresistor i'saap-A 01H3. SignaTtO vbemeasured.' AIlOtheTObjCt" Of phedtgthe Cathode"Circuitoffaxfrsttriggertub'egzi the invention `ris to vprovide 4means' for 'measuringi i.Tnecontroielectrode-of thenrst trigger-#tube the average'fleqllencyof anapplied Signal by" I is` connected -to-4 the'anodeof alsecondfdiodefpulsing saidsignal,l by applying'said pulS'eS" t0n tolone-A terminal'ofA thegr-idlfresistorxIS, and-to`==-- triggercircuit' and-'deriving acurrentfrom-'said '20f0ne-1-,ermi-na1 ofv theicapaitr |.3 Thacanhodee..trigger circuit which is proportional in amplitude Offthe/--Secondfdiode5 mld-V theremeinin'gftfgrmiefy t0 the' average frequency '0f theyapplied Signal nal` of the resistor` I5 areconnectedfto grou-ndiStille-Immer Objeci- S 1'10' PIOVida HOVeltI'ggeI The remaining terminalof-capacitor I3 iis-corr circuitfromjwhich may be'derived'a currentpro;- x nectedqto the anode of @Second-triggermpegs portionai inamplitude! to the average frequency "25" and to' oneterminal ofazresistanceinetworkfzs: of tliesignal applied tov key'the"trigger'CCUtThe remaining"inputterminaltof 'thefresistancelv The invention willlbedescribedherenaftfby" network2'3is connected' togasource'off.anode"pol-.2fv referenceto thefdrawings, of which Fiel iS e itenten forythe second. trigger. tube s.. Tnep'an'oue. Schematiccircuit-diagram 0f 'the invention; andi 0J, ofthe'rsttrigger tube Isconnectedtofthe.'cone' Fig..2 is a series ofgraphs indicating. the.vopera- 3 ""tr0ye1ctr0de0f the Second triggertube angina,` tonofvtheVal'OuS CiIGllt-COIHPOHGIIS- tofone terminal of.a.co.up1ing' resistor,I4.""T1ie' l'ilefellngA t0 Fg.- 1Sgna1s from anyy SuitableY remainingterminal of the..f-resistor rIIL-"is con, source,` which may include aplurality 0f.; frenected through theresistorV 25. to; a. sourccyof.`Vquency components, are applied to theinputtert I anode potentiellerthersttrigger tube fl; mina-Ism.` of afilter circuit 9 which is designed35' The Operai-,10nd the circutjsas follows; 113115,. to.pass thefrequency band t0 bemeasuredf Th@l desiredL frequency component of`theesignalfA to luce` output of theflter 9 isappled tO'theiglidcirmeasuredfisrderived'fromthe,lter-.9A and applied,- cuit of a firstthermonic` tube I. The grid, bias 130.15118.Conergye1ectmde.of.the,msutube.|. which... is adjusted to limit thefamplitude ofy the signalsY40,., provides. highl ampiieation, and,... because ofitsfw tofbemeasuredA in order to eliminate, aS `much saturation characteristics,clipsthe peaksoflf-tlriewA as.. possib1e, response. to extraneoussignals suchI signal wave.v Thesignal is further.'amplifiedandiVaShaIm0r1CS higher than the .fundamentalfreclipped:by4aisimilar-action:in thefseconritube;.2;/-y fluency.y The rstztubel is operatedatthesatu-y and.A applied as asignah of: substantially;'square-i`rationfportion of its static characteristic in order 451;,wavefforrnftothe input Othethird-tube. Whem toderive an output signalwhich-issubstantiallyv the-'switchiZiLis connected; to thezinductor1'IsI,.thei=;of square waveform. The signalis.furtherarn-v third tube.3is;0perated toShockxcitejthe buntem. pliiedaby ansecond. thermionic tuloev 2 Whichds*circuit comprising the natural resonant;characef alsooperated'rat-the'vsaiuraton point of. its staticteristicsiof-l.theinductor IcI', toi derive avseriesi'ofcharacteristic,inzorder tofurther improveV the 50.1,.A pulses of.decreasing:amplitudeyfromt eachzisquaree: square wave form ofthe signal.Thefsignal. offA wavepulse appliedito tha-circuit. Theaiirstidiotic:-ysubstantially,,squarefwave form isv next applied. 4 Drovidesconsiderabledampingof:theapulsesfaoff-vv toft'hey inputcircuitof a thirdthermionicitube-3.l decreasing; amplitudeto elirnirrate,fYsubstantiailThea-.anode circuit ofthe third tubey 3:.inc1udesff allrofrthe pulse'rsignals except .thezrs't positiver# a .twoi-positioniswitch, 20. whichis connectent` in; 55f

one position to one terminal of a resistor I9 andi* in another; positionto one termina1.of.e an.` inducr" ton I:I The-movable armzofthe'.switch#Macome-v nected'fto sthe.l cathode of a -first .f diode 4iandiv toz onezterminal .,of.- theqcapacitor 2 I. The,fremainin-gf;

terminalsA of .the vresistor I 9,v y.induotora I il anctgthe: f anodeotthefdiode., 4.are all connected .throughu anlanode. resistor; 24 to;thasource of high' po.;` The -f tential .for the;y anodev of the;third?, tubef: 3j

alternation. i' The resistance capacitw` networln f I9-2I acts as adiierentiating circuit. In this network the voltage across the resistorI9' will be substantially proportional to the rate of change of thesquare wave signal applied to the network and will therefore includeonly a sharp positive and negative pulse for each cycle of the squarewave signal. When the switch 20 is connected to the resistor I9, thedamping diode 4 may be omitted, since it will have little effect on thecircuit operation.

Signals derived from the circuit with either position of the switch 20are then applied as pulses to the control electrode of the peak amplier5. Ii desired, either the inductor Il or the resistor I9, and the switch20 may be omitted. The peak ampliiier is biased to amplify only thepositive peak portion of the pulse applied to the control electrode.Sharply peaked voltages from the cathode circuit of the peak amplier 5are applied to the input circuit of the first trigger tube 1.

The operation of the trigger circuit is as iollows: The rst trigger tube1 is biased so that it is normally conducting While the second triggertube 8 is biased so that it is normally non-conducting. When a positivepulse from 'the peak amplifier 5 is applied to the cathode of the rsttrigger tube l, the first trigger tube I is biased to cut-off and thesecond trigger tube 8 is made to conduct. This condition continues afterthe exciting pulse has passed, and until the grid of the first triggertube l, which has been driven to cut off by the charge on the capacitorI3, becomes sufciently positive for the rst trigger tube 'I to againbecome conducting and the second trigger tube 8 non-conducting. For asingle exciting pulse, the time during Which the second trigger tube 8will become conducting depends upon the capacitance of the capacitor I3,the grid capacitance ci the rst trigger tube 1, the resistance of theresistors I4 and I5, the cut-off voltage of the rst trigger tube 1, andthe rate of change of the maximum voltage on the anode ofthe secondtrigger tube 8 when the tube is suddenly made to conduct. Since all ofthese constants `can be calculated and Xed, the circuit can be adjustedto any desired time constant.

`The limit frequency of the circuit is dependent on the time requiredfor the trigger tubes to return to their normal bias condition afteractuation by an exciting pulse. This time interval may be greatlyreduced by the use of the second diode 6 which has a damping action onthe grid circuit of the first trigger tube 1 by providing substantialattenuation in the circuit when the grid of the rst trigger tube 'I isat positive potential. 'Ihe action of the diode 6 also tends to make theduration of the current pulse in the anode circuit of the second triggertube 8 more uniform. The amplitude of this pulse may be maintained at asubstantially constant level by proper voltage regulation of thepotentials applied to the trigger tube circuits. The current derivedfrom the output terminals I2 of the resistance network 23 will be afairly accurate indication of the average rate of occurrence of theexciting pulses applied to the cathode of the rst trigger tube 1.

Fig. 2a of the drawing shows a typical sine Wave signal applied to theinput circuit of the first saturation amplifier tube I. Fig. 2b shows asignal of substantially square wave form derived from the anode circuitof the second tube 2 and applied to the input circuit of the tube 3.Fig` 2c shows the wave Iform comprising pulses of diminishing amplitudederived from the tuned circuit ii when the switch 2G is connected to theinductor I i. The right-hand portion shows the wave-'form derived `fromthe differentiating network I', 2l when the switch 20 is connected tothe resistor I9. Fig. 2d shows the damping of the pulse current by therst diode Il. The portion of the graph above the dash line P indicatesthe positive portion of the pulse current which actuates the peakamplier 5. Fig. 2e shows the positive pulse derived from across theresistor 22 in the cathode circuit of the peak amplifier 5. Fig. 2gshows the potential variations on the grid of the first trigger tube lcaused by the application to the tube cathode of the pulse shown in Fig.2e. Fig. 2f' shows the corresponding potential variations in the anodecircuit of the second trigger tube 8 which are applied to the resistancenetwork 23. The dashed lines in Fig. 2g indicate the damping action ofthe second diode 6 and clearly show the action of this tube indecreasing the time required for the trigger tubes 'I and 8 to return totheir normal bias condition.

t should be understood that the iilter 9, tubes i, 2, l and 5, or any ofthem, may be omitted if the signal to be measured has suitablecharacteristics for the actuation of the trigger circuit comprising thetubes 6, and 8. It should also be understood that the second diode 6 maybe omitted if the operating frequency of the circuit is suliciently lowto permit the trigger tubes 1 and 8 to return to normal bias conditionwithout the damping action of the diode 6.

We claim as our invention:

l. The combination of means for producing an alternating voltage havinga flat-topped wave form, means for diierentiating said wave to pro ducevoltage pulses at the beginning and end of said wave, a detector havinga cathode and control grid, a resistor connected in series with saidcathode, means for biasing said grid to a predetermined negativepotential, means for applying said pulses to said grid, a multivibratorincluding iirst and second electron discharge elements having theirgrids and anodes cross-connected so that current conduction is normallyin the rst of said elements, means connecting said resistor between thegrid and cathode of the first of said elements so that currentconduction is temporarily transferred to the second of said elements inresponse to the voltage pulse detected by said detector, and a lowfrequency pass iilter connected in the anode circuit of the second ofsaid elements.

2. The combination of means for producing an alternating voltage havinga flat-topped wave form, means yfor differentiating said wave to producevoltage pulses at the beginning and end of said wave, a detector havinga cathode and control grid, a resistor connected in series with saidvcathode, means for biasing said grid to a predetermined negativepotential, means for applying said pulses to said grid, a multivibratorincluding rst and second electron discharge elements having their gridsand anodes cross-connected so that current conduction is normally inlthe iirst of said elements, means connecting said resistor between thegrid and cathode of the rst of said elements so that current conductionis temporarily :transferred to the second of said elements in responseto the voltage pulse detected by said detector, a second resistorconnected in the anode circuit of the second of said elements, and acircuit in parallel with said second resistor including a third resistorconnected in series Number Name Date with a, capacitor and a. fourthresistor. 2,063,025 Blumlein Dec. 8, 1936 JAN A. RAJCHMAN. 2,082,317Barber June 1, 1937 EDWIN A. GOLDBERG. 2,161,146 Echlin et a1 June 6,1939 5 2,221,591 Lansdale Nov. 12, 1940 REFERENCES CITED 2,266,401Reeves Dec. 16, 1941 2,272,070 Reeves Feb. 3, 1942 lhfftgerferens are ofrecord in the 2,307,316 Woiff Jan. 5, 1943 2,323,596 Hansell v July 6,1943 UNITED STATES PATENTS 1o 2,362,503 scott Nov. 14, 1944 Number NameDate 2,405,843 MOG Aug. 13, 1946y 1,933,219 Nakajima et al Oct. 31, 19332,061,734 Kell Nov. 24, 1936

